Question

QUESTION 1

The half-life for a reaction that is first-order in A is 15 minutes. How long will it take for the concentration of A to change from 0.16 M to 0.040 M?

A(g) →   B(g) + C(g)

		60 min
		45 min
		30 min
		23 min
		15 min

4 points   

QUESTION 2

When a 0.100 mol of a pure compound is dissolved in 1.0 L of water, the solution pH changes from 7.00 to 4.24. Which of the following is most likely the identity of the substance?

		A strong acid
		A strong base
		A weak acid
		A weak base
		A neutral salt

4 points   

QUESTION 3

Which of the following will NOT change if the temperature of a reaction system is changed?

		Frequency of molecular collisions
		Average kinetic energy of reactant molecules
		Reaction rate
		Rate constant
		Activation energy

4 points   

QUESTION 4

Which of the following best describes any reaction system where Q < K_c?

		The system will never be able to reach a state of equilibrium.
		The system is at equilibrium, and there are more products than reactants at equilibrium.
		The system is at equilibrium, and there are more reactants than products at equilibrium.
		The system is not at equilibrium, and the reaction will go in the reverse direction.
		The system is not at equilibrium, and the reaction will go in the forward direction.

4 points   

QUESTION 5

What is the equilibrium constant expression for K_c for the following heterogeneous equilibrium?

Ni(CO)₄(g) <----> Ni(s) + 4CO(g)

4 points   

QUESTION 6

Which of the following occurs when the temperature of a contained gas is reduced at constant volume?

		Pressure decreases
		Average molecular velocity decreases
		Average kinetic energy decreases
		Collision frequency decreases
		All of these

4 points   

QUESTION 7

Given a fixed amount of an ideal gas held at constant pressure, calculate the volume it would occupy if a 2.00 L sample were cooled from 60.0°C to 30.0°C.

		1.00 L
		4.00 L
		0.20 L
		1.82 L
		0.455 L

4 points   

QUESTION 8

Which of the following properties of liquids generally is lower for substances with stronger intermolecular forces?

		Viscosity
		Vapor pressure
		Boiling point
		Both viscosity and vapor pressure
		All of these

4 points   

QUESTION 9

Use the initial concentration and initial rate data in the table to determine the rate law for the reaction:  
A(aq) + B(aq)   →   C(aq) + D(g)

Experiment #	[A] (M)	[B] (M)	Initial Rate (M/s)
1	0.400	0.400	9.00×10-3
2	0.200	0.400	4.50×10-3
3	0.200	0.200	1.13×10-3

		Rate = k[A]
		Rate = k[B]2
		Rate = k[B]
		Rate = k[A]2[B]
		Rate = k[A][B]2

4 points   

QUESTION 10

If the hydronium ion concentration, [H₃O⁺], in a solution is 5.6×10⁻¹⁰M, what is the hydroxide ion concentration, [OH⁻], and the pH of the solution?

		[OH−] = 1.8×109 M, pH = 4.75
		[OH−] = 5.6×10−10M, pH = 10.56
		[OH−] = 1.0×10−7M, pH = 5.60
		[OH−] = 4.4×10−4M, pH = 9.25
		[OH−] = 1.8×10−5M, pH = 9.25

4 points   

QUESTION 11

Which of the following gases has the lowest average molecular velocity at the same temperature?

		Ne
		Xe
		N2
		F2
		All of these have the same average molecular velocity.

4 points   

QUESTION 12

In the following 2-step mechanism, which is the catalyst?

Step 1:   A + B  → C + D
Step 2:   B + C   → X + A

		A
		B
		C
		D
		X

4 points   

QUESTION 13

Which of the following substances has hydrogen bonding when in the pure liquid state?

		CH3-O-CH3
		NF3
		CH3OH
		HBr
		All of these have hydrogen bonding in the pure liquid state.

4 points   

QUESTION 14

Consider the following endothermic reaction at equilibrium in a 1-liter container:

2Cl₂(g) + 2H₂O(g) <----> 4HCl(g) + O₂(g)           ΔH > 0

Which of the following will cause a decrease in the equilibrium concentration of O₂?

		Increasing the temperature
		Adding Cl2 gas
		Adding HCl gas
		Adding O2
		Increasing the volume of the container

4 points   

QUESTION 15

Consider the following exothermic reaction at a state of equilibrium: C(s) + O₂(g) <----> CO₂(g) . Which of the following changes will cause value of the equilibrium constant K_c to change?

		Increasing the container volume
		Increasing the temperature
		Removing O2
		Adding solid carbon
		All of these

4 points   

QUESTION 16

Which of the following increases the solubility of a gas in solution?

		Increasing gas pressure and increasing temperature
		Increasing gas pressure and decreasing temperature
		Decreasing gas pressure and increasing temperature
		Decreasing gas pressure and decreasing temperature
		Adding more water

4 points   

QUESTION 17

When comparing a 1 m NaCl solution to that of pure water:

		The 1 m NaCl solution has a higher boiling point and the higher freezing point.
		The 1 m NaCl solution has a higher boiling point and a lower freezing point.
		The 1 m NaCl solution has a lower boiling point and a higher freezing point.
		The 1 m NaCl solution has a lower boiling point and a lower freezing point.
		They both have the same boiling point and freezing point.

4 points   

QUESTION 18

Which of the following types of solids have relatively low melting points, because melting these solids requires breaking intermolecular forces, not real bonds?

		Molecular solids
		Ionic solids
		Covalent-network solids
		Metallic solids
		Semiconductors

4 points   

QUESTION 19

Which of the following does NOT describe semiconductors?

		Their band gaps are between metals and insulators.
		Doped p-type and n-type semiconductors are less conductive than semiconductor materials that are not doped.
		Their band gaps increase as particle size decreases in the 1-10 nm range.
		They can be a single element or a compound.
		They usually have an average number of 4 valence electrons per atom.

4 points   

QUESTION 20

If the average rate of appearance of NH₃ in the following reaction is 1.40 M/s, what is the average rate of disappearance of H₂ during the same time period?

N₂(g) + 3H₂(g)  → 2NH₃(g)

		5.40 M/s
		2.80 M/s
		1.20 M/s
		0.700 M/s
		2.10 M/s

4 points   

QUESTION 21

Which of the following should be the most soluble in benzene, C₆H₆?

		CH3OH
		H2O2
		CCl4
		HF
		CH3NH2

4 points   

QUESTION 22

Which of the following best explains the relative boiling points for Cl₂ and HCl?

		Cl2 has the higher boiling point because liquid Cl2 has stronger London-dispersion forces than liquid HCl.
		Cl2 has the higher boiling point because liquid Cl2 has stronger dipole-dipole forces than liquid HCl.
		HCl has the higher boiling point because liquid HCl has hydrogen-bonding interactions while liquid Cl2 has no hydrogen bonding interactions.
		HCl has the higher boiling point because liquid HCl has dipole-dipole forces while liquid Cl2 does not have dipole-dipole forces.

4 points   

QUESTION 23

What is the density (g/L) of H₂ gas at a temperature of 283 K and 0.500 atm? (Hint: One approach is to assume a sample size of 1.0 L.)

		0.0107 g/L
		0.0217 g/L
		0.0434 g/L
		93.7 g/L
		0.0899 g/L

4 points   

QUESTION 24

Given that the molar volume of Ne gas is 22.414 L/mol at STP (1.00 atm of pressure and at a temperature of 273.15 K), predict the volume of H₂
gas when the number of moles is 2.50 mol under the same conditions of temperature and pressure.

		2.24 L
		56.0 L
		0.110 L
		5.60 L
		11.1 L

4 points   

QUESTION 25

Which of the following best describes a chemical reaction in a state of equilibrium?

		Reactant molecules are forming products as fast as product molecules are reacting to form reactants.
		The rate constants of the forward and reverse reactions (kf and kr) are equal.
		The value of the equilibrium constant, Kc, is 1.
		The limiting reagent has been consumed.
		All chemical reactions have stopped.

Answer 1

5) Kc = [CO]⁴ / [Ni(CO)₄]

6) At constant volume,

Pressure X volume = n X R X T

Pressure will be directly proportional to Temperature

so pressure will decrease

Also, Average molecular velocity decreases, Average kinetic energy decreases and Collision frequency decreases are directly proportional to temperature

so all of theses will decrease

7)

V1/T1 = V2/T2

2L / (60+273)K = V2 / (30+273)K

V2 = New volume = 1.82 Litres

8) Vapour pressure will be lower, for weak intermolecular forces

9) The rate decrease half on decreasing the concentration of A to half while it becomes 1/4 if the concentration of B decreases to half

so

Rate = K [A] [ B]²

10) [H3O+][OH-] = 10^-14

[OH-] = 10^-14 / 5.6 X 10^-10 = 1.78 X 10^-5

pH = -log(5.6 X 10^-10) = 9.25

11) Xe, as it has highest molecular weight

12) the catalyst gets regenerated

So answer is A

13) Only CH₃OH

14) Adding HCl

15) Only Increasing the temperature

16) Increasing gas pressure and increasing temperature

17) The 1 m NaCl solution has a higher boiling point and a lower freezing point.

18) Molecular solids

19) Doped p-type and n-type semiconductors are less conductive than semiconductor materials that are not doped.

20) average rate of appearnce of NH3 = 2/3 average rate of disapperance of H2

Therefore

average rate of disappearance of H₂ = 1.5 X 1.40 = 2.1 M /s

21) Non polar CCl₄

22) HCl has the higher boiling point because liquid HCl has dipole-dipole forces while liquid Cl₂ does not have dipole-dipole forces.

23) PV =nRT

n/V = P/RT

n/V = 0.5 / 0.0821 X 283 =0.0215 moles / Litre = 0.0215 X 2 grams / Litre = 0.043g / L

24) Volume = nRT / P

n = 2.5

P = 1atm

T = 273.15 K

R = 0.0821

Volume = 2.5 X 0.0821 X 273.15 / 1 = 56.064 L

25) Reactant molecules are forming products as fast as product molecules are reacting to form reactants.